Highlands Wilderness Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Highlands Wilderness Observatory clear sky chart from 2005-11-06 to 2025-07-21.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	17% 12% 4 9% 5% 4 4 3 5% 6% 31%	120697
	Night	17% 13% 5% 10% 5% 4 4 3 5% 6% 29%	118392
Transparency	Day	53% 6% 10% 20% 10% 1	124322
	Night	54% 6% 10% 19% 10% 1	122927
Seeing	Day	24% 14% 31% 19% 8% 3	15460
	Night	24% 12% 30% 24% 10% 1	24519

By Month

Percentage Cloud Cover NE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	13% 16% 6% 12% 5% 5% 4 4 4 5% 24%	3597
	11th to 20th	Day	11% 20% 9% 16% 9% 7% 5% 3 3 3 13%	3680
	21st to end	Day	14% 19% 9% 15% 6% 4 5% 3 4 4 18%	4466
February	1st to 10th	Day	14% 17% 7% 16% 7% 5% 4 3 4 4 20%	1800
	11th to 20th	Day	14% 15% 6% 15% 6% 4 4 3 4 4 24%	1753
	21st to end	Day	16% 18% 6% 11% 5% 6% 4 3 4 5% 21%	1529
March	1st to 10th	Day	19% 14% 5% 10% 6% 4 4 3 4 6% 26%	4883
	11th to 20th	Day	13% 15% 6% 9% 6% 5% 5% 4 5% 6% 25%	4980
	21st to end	Day	19% 14% 4 8% 4 3 3 2 3 4 35%	5482
April	1st to 10th	Day	21% 15% 4 6% 4 4 4 3 5% 6% 29%	2400
	11th to 20th	Day	23% 12% 3 6% 4 3 4 2 4 4 35%	2424
	21st to end	Day	22% 11% 4 7% 4 4 4 3 4 5% 33%	2600
May	1st to 10th	Day	21% 8% 3 7% 5% 5% 4 3 5% 6% 33%	6069
	11th to 20th	Day	18% 9% 2 7% 5% 4 4 3 5% 7% 35%	6318
	21st to end	Day	21% 9% 3 6% 4 5% 4 4 5% 7% 34%	6949
June	1st to 10th	Day	20% 8% 3 7% 5% 4 5% 4 5% 8% 32%	2800
	11th to 20th	Day	14% 7% 3 7% 5% 5% 5% 4 6% 9% 36%	2800
	21st to end	Day	18% 7% 2 7% 5% 5% 4 4 6% 8% 35%	2981
July	1st to 10th	Day	12% 5% 2 7% 5% 5% 5% 5% 7% 11% 36%	4651
	11th to 20th	Day	12% 6% 2 5% 4 5% 5% 4 6% 8% 43%	4580
	21st to end	Day	9% 6% 2 6% 5% 4 5% 5% 7% 9% 44%	4700
August	1st to 10th	Day	16% 8% 3 8% 5% 4 5% 4 6% 8% 34%	4104
	11th to 20th	Day	16% 7% 3 6% 5% 4 5% 4 7% 9% 34%	4044
	21st to end	Day	10% 5% 2 6% 5% 4 5% 4 7% 10% 42%	4322
September	1st to 10th	Day	15% 7% 2 7% 5% 4 4 3 5% 8% 39%	2280
	11th to 20th	Day	13% 6% 2 6% 4 4 4 3 5% 7% 46%	2228
	21st to end	Day	18% 8% 3 7% 4 4 5% 3 5% 6% 37%	2014
October	1st to 10th	Day	20% 10% 2 8% 5% 4 4 3 4 7% 32%	1900
	11th to 20th	Day	25% 11% 3 8% 5% 4 5% 4 5% 6% 24%	1900
	21st to end	Day	28% 13% 4 8% 5% 4 4 2 4 6% 22%	2090
November	1st to 10th	Day	17% 12% 4 7% 5% 6% 4 3 5% 6% 31%	1627
	11th to 20th	Day	17% 15% 4 10% 5% 5% 4 4 6% 6% 24%	1600
	21st to end	Day	21% 21% 5% 10% 5% 4 5% 3 4 5% 17%	1600
December	1st to 10th	Day	17% 26% 8% 11% 5% 4 3 4 5% 4 14%	2600
	11th to 20th	Day	19% 21% 6% 15% 4 3 3 2 3 3 20%	2986
	21st to end	Day	24% 21% 6% 13% 4 3 3 2 3 4 19%	3960
January	1st to 10th	Night	15% 18% 8% 12% 6% 5% 4 3 5% 5% 19%	6349
	11th to 20th	Night	12% 16% 8% 21% 8% 6% 5% 3 4 4 13%	6201
	21st to end	Night	13% 19% 9% 14% 5% 6% 4 3 4 4 18%	6490
February	1st to 10th	Night	13% 16% 6% 13% 8% 6% 5% 4 5% 5% 19%	2600
	11th to 20th	Night	13% 15% 7% 12% 6% 6% 5% 3 4 4 25%	2533
	21st to end	Night	15% 16% 5% 10% 7% 5% 4 4 5% 5% 25%	2100
March	1st to 10th	Night	17% 14% 4 12% 5% 4 4 3 4 5% 28%	4955
	11th to 20th	Night	10% 14% 6% 9% 5% 5% 5% 4 6% 7% 28%	4979
	21st to end	Night	20% 10% 3 8% 4 4 4 3 6% 6% 32%	5450
April	1st to 10th	Night	21% 13% 4 9% 4 5% 4 3 5% 5% 29%	2000
	11th to 20th	Night	18% 10% 3 7% 4 4 3 4 5% 6% 36%	1942
	21st to end	Night	19% 11% 3 9% 4 4 4 4 5% 5% 33%	1800
May	1st to 10th	Night	23% 6% 3 7% 5% 5% 5% 3 5% 6% 34%	3870
	11th to 20th	Night	15% 7% 3 6% 4 4 4 3 5% 7% 42%	3575
	21st to end	Night	19% 8% 2 6% 4 4 4 3 4 7% 37%	3926
June	1st to 10th	Night	16% 8% 2 6% 5% 4 5% 4 7% 8% 36%	1600
	11th to 20th	Night	12% 7% 2 5% 4 5% 5% 4 6% 8% 43%	1600
	21st to end	Night	16% 7% 3 7% 4 5% 5% 3 5% 7% 39%	1406
July	1st to 10th	Night	10% 5% 2 7% 5% 5% 5% 4 7% 7% 44%	2521
	11th to 20th	Night	15% 6% 1 5% 4 3 4 3 5% 7% 47%	2600
	21st to end	Night	10% 6% 2 5% 3 4 4 4 6% 7% 49%	2850
August	1st to 10th	Night	12% 5% 2 5% 4 3 4 4 6% 7% 47%	2825
	11th to 20th	Night	15% 6% 3 6% 4 4 4 3 5% 7% 43%	2785
	21st to end	Night	14% 5% 1 5% 4 3 4 3 5% 6% 49%	3302
September	1st to 10th	Night	13% 6% 2 6% 5% 3 4 4 6% 7% 45%	1900
	11th to 20th	Night	13% 6% 2 4 4 3 3 3 5% 7% 50%	1949
	21st to end	Night	18% 8% 2 6% 4 5% 3 3 5% 5% 41%	2165
October	1st to 10th	Night	18% 8% 2 7% 5% 4 4 3 5% 6% 37%	2280
	11th to 20th	Night	23% 12% 3 7% 5% 4 4 3 5% 6% 28%	2280
	21st to end	Night	23% 13% 4 9% 5% 4 4 3 5% 5% 26%	2508
November	1st to 10th	Night	20% 11% 3 6% 5% 4 4 3 4 6% 34%	2667
	11th to 20th	Night	18% 15% 4 7% 6% 4 4 3 5% 6% 27%	2800
	21st to end	Night	22% 16% 5% 9% 6% 5% 5% 3 5% 6% 19%	2800
December	1st to 10th	Night	20% 22% 7% 12% 5% 4 4 3 4 5% 14%	4580
	11th to 20th	Night	17% 22% 7% 15% 5% 4 4 3 4 5% 15%	5208
	21st to end	Night	24% 20% 6% 14% 5% 4 3 2 3 4 15%	6996

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	59% 6% 9% 17% 9%	3598
	11th to 20th	Day	74% 7% 5% 8% 6%	3710
	21st to end	Day	70% 4 7% 10% 8% 1	4466
February	1st to 10th	Day	69% 3 7% 15% 4 1	1800
	11th to 20th	Day	62% 5% 8% 14% 9% 1	1762
	21st to end	Day	65% 4 9% 13% 8% 1	1529
March	1st to 10th	Day	60% 5% 11% 10% 14% 1	4886
	11th to 20th	Day	57% 5% 12% 17% 7% 2	4980
	21st to end	Day	53% 4 6% 19% 15% 2	5482
April	1st to 10th	Day	57% 4 7% 19% 11% 2	2400
	11th to 20th	Day	53% 5% 7% 20% 15% 1	2424
	21st to end	Day	54% 4 7% 19% 12% 3	2600
May	1st to 10th	Day	51% 5% 8% 21% 10% 5%	6078
	11th to 20th	Day	48% 7% 9% 18% 18% 1	6322
	21st to end	Day	50% 5% 11% 20% 12% 3	6949
June	1st to 10th	Day	50% 6% 9% 21% 14%	2800
	11th to 20th	Day	43% 6% 11% 26% 13% 2	2800
	21st to end	Day	47% 6% 12% 22% 11% 1	2981
July	1st to 10th	Day	39% 7% 16% 25% 12% 1	4581
	11th to 20th	Day	37% 5% 15% 32% 10%	4505
	21st to end	Day	36% 7% 12% 33% 12%	4550
August	1st to 10th	Day	46% 7% 12% 25% 9% 1	4091
	11th to 20th	Day	44% 8% 13% 27% 8%	4083
	21st to end	Day	35% 7% 12% 35% 11% 1	4322
September	1st to 10th	Day	43% 5% 13% 28% 11% 1	2280
	11th to 20th	Day	37% 5% 13% 31% 13% 1	2228
	21st to end	Day	48% 5% 12% 24% 11%	2014
October	1st to 10th	Day	46% 5% 11% 28% 10% 1	3160
	11th to 20th	Day	51% 6% 12% 20% 10% 1	3140
	21st to end	Day	58% 6% 12% 19% 5%	3428
November	1st to 10th	Day	53% 6% 13% 20% 7% 1	1627
	11th to 20th	Day	59% 6% 12% 14% 7% 2	1600
	21st to end	Day	69% 6% 10% 10% 5% 1	1600
December	1st to 10th	Day	74% 4 11% 9% 3	2600
	11th to 20th	Day	71% 4 7% 13% 5%	2986
	21st to end	Day	71% 4 6% 12% 7%	3960
January	1st to 10th	Night	66% 5% 7% 14% 7%	6349
	11th to 20th	Night	72% 7% 7% 7% 5% 1	6246
	21st to end	Night	68% 6% 8% 9% 9% 1	6490
February	1st to 10th	Night	65% 5% 8% 16% 5% 1	2600
	11th to 20th	Night	61% 5% 8% 17% 8% 1	2535
	21st to end	Night	60% 4 9% 19% 8%	2100
March	1st to 10th	Night	58% 5% 8% 14% 12% 4	4965
	11th to 20th	Night	53% 7% 15% 17% 8% 1	4980
	21st to end	Night	51% 5% 8% 20% 14% 2	5450
April	1st to 10th	Night	57% 5% 7% 18% 11% 2	2000
	11th to 20th	Night	49% 5% 7% 22% 15% 1	1942
	21st to end	Night	52% 6% 9% 16% 16% 2	1800
May	1st to 10th	Night	51% 4 10% 17% 13% 5%	3877
	11th to 20th	Night	41% 7% 12% 22% 17% 2	3576
	21st to end	Night	46% 6% 10% 23% 13% 1	3927
June	1st to 10th	Night	44% 6% 10% 23% 15% 2	1600
	11th to 20th	Night	39% 6% 11% 25% 19% 1	1600
	21st to end	Night	44% 7% 13% 22% 13% 1	1406
July	1st to 10th	Night	36% 6% 15% 25% 16% 1	2481
	11th to 20th	Night	35% 6% 11% 33% 14%	2552
	21st to end	Night	33% 6% 13% 33% 15% 1	2759
August	1st to 10th	Night	35% 5% 16% 26% 17% 1	2814
	11th to 20th	Night	39% 7% 18% 24% 12% 1	2812
	21st to end	Night	35% 5% 12% 34% 12% 2	3302
September	1st to 10th	Night	37% 6% 15% 27% 13% 1	1900
	11th to 20th	Night	34% 5% 13% 34% 14% 1	1949
	21st to end	Night	45% 5% 10% 29% 11%	2165
October	1st to 10th	Night	38% 5% 10% 28% 19%	3800
	11th to 20th	Night	48% 6% 13% 24% 9%	3779
	21st to end	Night	52% 6% 14% 21% 7%	4120
November	1st to 10th	Night	52% 5% 12% 22% 9%	2667
	11th to 20th	Night	57% 5% 13% 16% 8% 1	2800
	21st to end	Night	65% 6% 12% 12% 4	2800
December	1st to 10th	Night	73% 5% 11% 9% 3	4580
	11th to 20th	Night	72% 4 9% 10% 5%	5208
	21st to end	Night	74% 4 6% 10% 6%	6996

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	24% 21% 36% 13% 6% 2	200
	11th to 20th	Day	26% 22% 32% 15% 2 2	223
	21st to end	Day	25% 16% 40% 13% 4 1	330
February	1st to 10th	Day	29% 27% 32% 9% 3	300
	11th to 20th	Day	29% 27% 37% 6% 1	300
	21st to end	Day	38% 20% 32% 11%	293
March	1st to 10th	Day	27% 19% 36% 15% 2	500
	11th to 20th	Day	29% 18% 34% 15% 3 1	500
	21st to end	Day	35% 16% 31% 13% 5%	550
April	1st to 10th	Day	30% 22% 28% 14% 5% 1	500
	11th to 20th	Day	38% 15% 23% 14% 6% 3	492
	21st to end	Day	31% 17% 32% 12% 7% 1	500
May	1st to 10th	Day	28% 14% 29% 19% 6% 5%	503
	11th to 20th	Day	21% 14% 34% 18% 11% 3	527
	21st to end	Day	21% 13% 31% 20% 10% 5%	573
June	1st to 10th	Day	25% 11% 33% 23% 7% 2	530
	11th to 20th	Day	17% 13% 32% 25% 9% 4	530
	21st to end	Day	23% 11% 32% 24% 8% 2	711
July	1st to 10th	Day	11% 10% 34% 27% 14% 5%	570
	11th to 20th	Day	16% 7% 28% 29% 14% 6%	524
	21st to end	Day	12% 10% 33% 28% 11% 6%	532
August	1st to 10th	Day	16% 5% 30% 27% 15% 6%	486
	11th to 20th	Day	15% 7% 24% 27% 19% 7%	479
	21st to end	Day	15% 10% 31% 23% 14% 7%	539
September	1st to 10th	Day	16% 11% 29% 23% 14% 6%	490
	11th to 20th	Day	13% 7% 24% 23% 21% 12%	490
	21st to end	Day	22% 13% 24% 24% 11% 5%	490
October	1st to 10th	Day	25% 14% 26% 17% 16% 3	490
	11th to 20th	Day	27% 18% 33% 16% 5% 1	490
	21st to end	Day	35% 16% 30% 16% 4	539
November	1st to 10th	Day	28% 19% 30% 18% 5%	259
	11th to 20th	Day	31% 21% 31% 15% 2 2	200
	21st to end	Day	33% 17% 40% 8% 3 1	200
December	1st to 10th	Day	34% 17% 30% 19% 2 1	200
	11th to 20th	Day	38% 22% 25% 13% 3 1	200
	21st to end	Day	36% 18% 31% 11% 3 1	220
January	1st to 10th	Night	32% 18% 30% 15% 5%	800
	11th to 20th	Night	29% 15% 32% 18% 6% 1	800
	21st to end	Night	21% 14% 34% 23% 6% 1	880
February	1st to 10th	Night	25% 21% 33% 19% 2	800
	11th to 20th	Night	24% 19% 35% 18% 4	783
	21st to end	Night	27% 20% 30% 20% 3	660
March	1st to 10th	Night	25% 18% 35% 19% 3	800
	11th to 20th	Night	23% 17% 35% 19% 4 1	800
	21st to end	Night	24% 12% 33% 22% 9%	880
April	1st to 10th	Night	29% 16% 31% 19% 5%	800
	11th to 20th	Night	27% 14% 31% 20% 8% 1	758
	21st to end	Night	25% 10% 33% 22% 9%	600
May	1st to 10th	Night	23% 6% 28% 28% 12% 2	521
	11th to 20th	Night	18% 7% 35% 29% 11%	394
	21st to end	Night	16% 5% 31% 35% 12% 1	433
June	1st to 10th	Night	19% 5% 32% 34% 10% 1	400
	11th to 20th	Night	15% 10% 26% 37% 12%	400
	21st to end	Night	19% 7% 25% 36% 13% 1	400
July	1st to 10th	Night	10% 6% 26% 42% 16% 1	390
	11th to 20th	Night	13% 4 27% 34% 22% 1	388
	21st to end	Night	11% 3 25% 40% 20%	478
August	1st to 10th	Night	13% 4 19% 36% 26% 2	567
	11th to 20th	Night	11% 6% 17% 36% 27% 3	564
	21st to end	Night	15% 5% 27% 30% 21% 2	727
September	1st to 10th	Night	14% 8% 29% 29% 18% 4	760
	11th to 20th	Night	16% 4 23% 31% 23% 4	760
	21st to end	Night	23% 8% 20% 30% 16% 3	760
October	1st to 10th	Night	23% 10% 26% 25% 15% 1	760
	11th to 20th	Night	30% 13% 26% 22% 9% 1	760
	21st to end	Night	30% 13% 31% 21% 4	836
November	1st to 10th	Night	28% 12% 28% 24% 9% 1	780
	11th to 20th	Night	28% 15% 33% 17% 5% 1	800
	21st to end	Night	31% 14% 30% 21% 4 1	800
December	1st to 10th	Night	34% 18% 29% 14% 5%	800
	11th to 20th	Night	28% 18% 33% 17% 3 1	800
	21st to end	Night	34% 14% 31% 18% 3	880

Page generated at 2025-07-18 01:09:59. Version ac07

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